[Kubernetes][Rancher] Secure Websocket Error

Hi there,
after searching hours and hours for solutions, i finally guess i need to either give up or ask a question here,s o sorry for that.
I am running a traefik instance (2.3) on Kubernetes to proxy different applications and provide secure connections via letsencrypt certificates. One of the applications is a rancher v2 (2.4.2) instance, which is working fine so far, the UI is working.
Sadly secure websocket connections are not working as expected, for example a cattle-node-agent (rancher) is giving errors like that:

"Failed to connect to proxy. Response status: 200 - 200 OK
error="websocket: bad handshake"

Secure connections are following this flow:
agent -> Loadbalancer (OTC ELB), tcp -> traefik instance -> rancher service -> rancher pod/container

So https is working fine, but wss is not. Is there anybody able to provide some guidance/help?

Thanks in advance!

I am having this exact same problem. @sfhl did you find a way to fix this?